The present invention relates to a gas tank arrangement for a dual fuel internal combustion engine for a vehicle. The invention also relates to a vehicle comprising such a gas tank arrangement. The invention is applicable on vehicles, in particularly low, medium and heavy duty vehicles commonly referred to as trucks. Although the invention will mainly be described in relation to a truck, it may also be applicable for other type of vehicles such as e.g. working machines, cars, etc.
In relation to propulsion systems for heavy duty vehicles, internal combustion engines are frequently used. These internal combustion engines are most often propelled by a combustible fuel such as e.g. diesel or petrol. However, in order to further reduce engine emissions of the vehicles, alternative propulsion methods and/or fuels are being used, either alone or in combination with the well known combustible feels. These may include, for example, ethanol or electrical propulsion from an electric machine, etc.
As a further alternative, a combustible gas, such as e.g. compressed natural gas, DME, biogas, etc. has been found a suitable propulsion fuel for vehicles in the form of trucks. The combustible gas can be used in combination with the combustible fuel for propelling the internal combustion engine, in the following referred to as a dual fuel internal combustion engine. Since the residuals from the combustible gas are relatively environmentally friendly in comparison to e.g. combustible fuels, pollution from the emissions thereof are reduced for these types of engines.
A problem with engines being propelled by the above described combustible gas is that if leakage of gas occurs from e.g. the gas tank or other positions of the system prior to combustion thereof, there is a risk of green house gas emission pollution. Unwanted leakage of this kind also has an economical aspect since the fuel consumption will increase. There is thus a need to further improve the gas tank arrangements for dual fuel internal combustion engines.
It is desirable to provide a gas tank arrangement which at least partially overcomes the deficiencies of the prior art.
According to a first aspect of the present invention, there is provided a gas tank arrangement for a dual fuel internal combustion engine, the gas-tank arrangement comprising a gas tank for containing a combustible gas, wherein the gas tank arrangement further comprises an additional gas tank downstream said gas tank, wherein the additional gas tank is configured to be arranged in upstream fluid communication with an air inlet of the dual fuel internal combustion engine for delivery of combustible gas to the dual fuel internal combustion engine via said air inlet.
The wording “combustible gas” should in the following and throughout the entire description be interpreted as a gas which can be ignited, either self-ignited by compression or be ignited by e.g. a spark plug. The invention should thus not be limited to any specific combustible gas. However, as a non-limiting example, the combustible gas may be natural gas, which is described farther below. Other alternatives are of course conceivable such as e.g. DME or biogas, etc. The combustible gas which can be provided in the gas tank can be in liquid phase and in gas phase. Hence, the wording “combustible gas” should be interpreted to include liquefied gas as well as gas in gas phase. Accordingly, a lower portion of the gas tank can be provided with liquid combustible gas while an upper portion of the gas tank can be provided with combustible gas in gas phase.
Furthermore, the air inlet of the dual fuel internal combustion engine should be understood to mean the inlet where air is provided to the inlet manifold of the combustion engine. It should also be understood to mean the inlet manifold itself. Hence, the combustible gas can be delivered to the dual fuel internal combustion engine from the additional gas tank as a mixture with air at the inlet manifold.
As described above, the combustible gas may be in a liquid phase and in a gas phase. The wording “fluid communication” should therefore in the following and throughout the entire description be interpreted as a fluid communication for both liquids and gases.
An advantage of the present invention is that the fuel consumption for the dual fuel internal combustion engine is improved. The reason is that prior to refill of the gas tank, the pressure level of the gas tank can be reduced by delivery of combustible gas to the additional gas tank instead of venting the gas tank and deliver excess gas to e.g. the tank station or to the ambient environment, as has been done in prior art solutions. Accordingly, excess gas can be taken cared of by the additional gas tank when venting the gas tank. The gas tank arrangement is thus more environmentally friendly since excess gas from the gas tank can be stored in the additional gas tank instead of ventilation to the ambient environment.
Furthermore, by arranging the additional gas tank in fluid communication with the air inlet of the dual fuel internal combustion engine, the pressure level demands on the additional gas tank can be reduced. When delivering combustible gas to the dual fuel internal combustion engine via the air inlet, the pressure demands are lower compared to delivery of combustible gas to the fuel injectors of the dual fuel internal combustion engine for the propulsion function thereof.
According to an example embodiment, the gas tank arrangement may comprise a compressor arranged in fluid communication between the gas tank and the additional gas tank.
Hereby, the combustible gas delivered from the gas tank to the additional gas tank can be pressurized to a predetermined limit. An advantage of pressurizing the combustible gas is that more gas can be stored/contained in the additional gas tank. Also, it may be necessary to overcome the pressure generated by the turbine compressor of the dual fuel internal combustion engine. Furthermore, the compressor can be controlled by a control unit for controllably delivery of combustible gas to the additional gas tank. For example, the compressor may be controlled to deliver combustible gas to the additional gas tank during predetermined conditions. Such predetermined conditions may, for example, be that the additional gas tank has sufficient space to receive further combustible gas, or that the pressure in the gas tank is too high and the gas tank is in need of ventilation, etc.
According to an example embodiment, the gas tank arrangement may comprise a control valve positioned downstream the additional gas tank.
Hereby, the dual fuel internal combustion engine can controllably be provided with combustible gas from the additional gas tank. Thus, the dual fuel internal combustion engine can receive combustible gas from the additional gas tank when the conditions for doing so are beneficial. The control valve may, for example, be controlled by the above described control unit. Accordingly, the control valve is thus configured to be positioned in fluid communication between the addition gas tank and the air inlet of the dual fuel internal combustion engine. The conditions beneficial for receiving combustible gas from the additional gas tank to the air inlet of the dual fuel internal combustion engine may comprise e.g. sufficient engine temperature and sufficient operation of an engine after treatment system, etc.
According to an example embodiment, the gas tank arrangement may comprise a gas conduit in fluid communication with the gas tank and configured to be arranged in fluid communication with the fuel injection system of the dual fuel internal combustion engine for supply of combustible gas front the gas tank.
Hereby, the dual fuel internal combustion engine can be propelled by combustible gas also via the fuel injection system.
According to an example embodiment, the gas conduit may comprise means for converting liquefied combustible gas to compressed combustible gas.
Hereby, the combustible gas can be provided in liquid phase from the gas tank and thereafter converted into pressurized gas phase which is suitable for delivery to the fuel injection system. The gas conduit can thus be provided in connection to the lower portion of the gas tank.
According to an example embodiment, the means for converting liquefied combustible gas to compressed combustible gas may comprise a fuel pump and an evaporating unit in downstream fluid communication with said fuel pump.
The wording evaporating unit should be understood to mean a device or arrangement which converts a fluid from a liquid phase to a gas phase. Such evaporating unit may, as a non-limiting example, be a heat exchanger.
The fuel pump thus pressurizes the liquid combustible gas before delivery to the evaporating unit, which transforms the compressed liquefied gas to compressed gas phase prior to delivery to the fuel injection system of the dual fuel internal combustion engine.
According to an example embodiment, the gas tank arrangement may comprise a valve arrangement downstream the means for converting liquefied combustible gas to compressed combustible gas. The valve arrangement may, for example, be a pressure regulator controlled by the above described control unit or another control unit of the vehicle.
According to an example embodiment, the gas tank arrangement may comprise a return conduit positioned downstream the means for converting liquefied combustible gas to compressed combustible gas and arranged in upstream fluid communication with the gas tank.
An advantage of the return conduit is that pressurized combustible gas can be redirected to the gas tank when, for example, the dual fuel internal combustion engine has been shut off. Hereby, there is a reduced risk of accidental gas delivery to the fuel system, such as the diesel system, of the vehicle.
According to an example embodiment, the return conduit may be positioned in fluid communication between the valve arrangement and the gas tank.
Hereby, the valve arrangement can be controlled to either deliver combustible gas to the fuel injection system of the dual fuel internal combustion engine or back to the gas tank.
Accordingly, and according to an example embodiment, the valve arrangement may be configured to controllably provide compressed combustible gas to the fuel injection system of the duel fuel internal combustion engine and to the gas tank.
According to an example embodiment, the gas tank arrangement may comprise a compressed combustible gas tank downstream the means for converting liquefied combustible gas to compressed combustible gas.
Hereby, a storage tank for high-pressure combustible gas is provided which can deliver high-pressure combustible gas to the fuel injection system of the dual fuel internal combustion engine when desired.
According to an example embodiment, the gas tank may be a gas pressure vessel. According to an example embodiment the additional gas tank may be an additional gas pressure vessel. It should be readily understood that also the compressed combustible gas tank may be gas pressure vessels. Pressure vessels are advantageous since they can store and contain high-pressure gas.
According to an example embodiment, the combustible gas may be natural gas. Natural gas is a well known combustible gas which, at present, can be provided at a plurality of gas stations.
According to a second aspect of the present invention, there is provided a vehicle comprising a dual fuel internal combustion engine, a feel tank and a gas tank arrangement according to any of the above described example embodiments of the first aspect of the present invention, wherein the dual fuel internal combustion engine is arranged downstream the fuel tank and the gas tank arrangement.
Effects and features of this second aspect are largely analogous to those described above in relation to the first aspect of the present invention.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.